1. Field of the Invention
The invention relates to a sintered nuclear fuel compact of UO.sub.2 or the mixed oxides (U, Pu)O.sub.2 and (U, Th)O.sub.2, with a neutron poison that is incorporated in the sintered matrix, as well as a method for producing this sintered nuclear fuel compact.
2. Description of the Prior Art
A sintered nuclear fuel compact of this kind along with a method for its production is known from German Pat. No. 31 44 684 and related U.S. Pat. No. 4,512,939. The neutron poison comprises a rare earth element, in particular gadolinium. To produce this sintered nuclear fuel compact, UO.sub.2 starting powder is mixed with rare earth oxide powder (Gd.sub.2 O.sub.3) and the mixture is compressed into a compact, which is subjected to a heat treatment in the temperature range of from 1500.degree. C. to 1750.degree. C. in a sintering atmosphere having a reducing effect. The holding time for this temperature may be in the range from one hour to ten hours, while the heating speed of the compact may be in the range from 1.degree. C. per minute to 10.degree. C. per minute.
Fuel rods of nuclear reactor fuel elements are filled with sintered nuclear fuel compacts of this kind. The rare earth elements and gadolinium in particular are neutron poisons that can be burned up in terms of neutron physics and that lose their neutron-poisoning property after a certain period of use of the nuclear fuel element in a nuclear reactor. A nuclear fuel element is for example used in the nuclear reactor over the course of three successive fuel element cycles, which are typically of equal length. At the end of one fuel element cycle, some of the fuel elements in a nuclear reactor are replaced with fresh unirradiated nuclear fuel elements. If the fuel element cycles are relatively long, the rare earth elements, and the gadolinium in particular, in the fuel elements freshly introduced into the nuclear reactor do not burn up completely by the end of their first fuel element cycle. A so-called residual poisoning remains, which causes undesirable losses in reactivity at the beginning of the next fuel element cycle in the nuclear reactor.